Method and apparatus for continuously casting hollow rounds

ABSTRACT

A method and apparatus for continuously casting a hollow round for manufacturing seamless tubing. Apparatus includes an openended tubular water-cooled mold and a tubular water-cooled lance suspended within the mold, leaving an annular cavity therebetween. Molten metal is poured into the cavity. Outside and inside skins solidify on the metal, at first leaving a liquid core between the two skins. There is a problem that the inside skin tends not to remain concentric with the outside skin. Invention provides magnetic means acting on plugs within the inside skin to hold the two skins in a concentric relation.

United States Patent [151 3,661,196 Kummant 1 May 9, 1972 54] METHOD ANDAPPARATUS FOR 2,600,254 6/1952Lysobey...................,........lS/DIG. 33 CONTINUOUSLY CASTINGHOLLOW 3,428,371 2/1969 Lyman.. ..308/l0 ROUNDS 3,487,876 l/l970 Bucci..l64/282 X [72] inventor: Karl E. Kumrnant, Amherst, Ohio [73]Assignee: United States Steel Corporation [22] Filed: Oct. 2, 1970 [2|]Appl. No.: 77,470

[52] [1.5. CI ..l64/85,164/l48, l64/28l,

164/282, l8/DlG. 33

[5 l] Int. Cl ..B22d 11/02 [58] Field of Search 1 64/85, 146-148,164/281, 282; l8/DIG. 33

[56] References Cited UNITED STATES PATENTS 2,324,645 7/1943 Prehler..l8/DlG. 33

- SCILL A 71/18 Ul'tIMN/SI Primary Examiner-Robert D. BaldwinAltorneywalter P. Wood [57] ABSTRACT A method and apparatus forcontinuously casting a hollow round for manufacturing seamless tubing.Apparatus includes an open-ended tubular water-cooled mold and a tubularwater-cooled lance suspended within the mold, leaving an annular cavitytherebetween. Molten metal is poured into the cavity. Outside and insideskins solidify on the metal, at first leaving a liquid core between thetwo skins. There is a problem that the inside skin tends not to remainconcentric with the outside skin, Invention provides magnetic meansacting on plugs within the inside skin to hold the two skins in aconcentric relation.

9 Chins, 7 Drawing Figures CO Qv PATENTEnm 9 m2 ll/ENTOR KARL E. KUHMANTh is Attorney PATENTEDMAY 9:972 3661.196 sum 3 0F 3 LL? FYI; s

INVENTOR POWER sol/RC5 KARL E. KUMMANT re ay fl is A Home METHOD ANDAPPARATUS FOR CONTINUOUSLY CASTING HOLLOW ROUNDS This invention relatesto an improved method and apparatus for continuously casting hollowrounds of metal for manufacture of seamless tubing.

One type of apparatus for continuously casting metal products of solidcross section includes a water-cooled mold open at both ends, trains ofvertically spaced guide rolls below the mold, a set of power-drivenpinch rolls below the guide rolls, and a curved casting guide below thepinch rolls. Before a casting operation begins, a starter bar isinserted upwardly through the pinch rolls and guide rolls to the mold. Astream of molten metal is poured through the mold into contact with thetop of the starter bar, which descends through the guide rolls and pinchrolls ahead of the casting. A skin of metal solidifies on the outside ofthe casting within the mold, but the core at first remains liquid. Asthe casting passes the guide rolls, water sprays are applied to itssurface, whereby the core progressively solidifies. Initially theleading end of the casting attaches itself to the top of the starterbar, but the starter bar is disconnected as the casting passes throughthe pinch rolls. At first the pinch rolls restrain descent of thestarter bar, but after the casting is part way through the guide rolls,the pinch rolls propel the starter bar and casting. After the starterbar is disconnected, bending rolls within the casting guide bend thecasting 90 so that it travels horizontally from there on for furtherprocessing. Reference can be made to Foldessy, U.S. Pat. No. 3,338,297for a more complete showing of such apparatus.

Efforts to apply analogous procedures to the continuous casting ofhollow rounds have not been successful. If a lance or mandrel ispositioned within the mold to provide an annular cavity in which thehollow round is formed, there is a problem in cooling and solidifyingthe inside surface of the casting. When an inside skin solidifies, anannular liquid core remains between the inside and outside skins, whichcore does not solidify throughout until the casting descends asubstantial distance below the mold. This leads to another problem thatit is difficult to maintain the inside skin in a concentric relationwith the outside skin before the intervening core fully solidi fies.Unless the two skins remain concentric, the hollow round does not havewalls of uniform thickness, and is not acceptable for manufacture ofseamless tubing.

An object of my invention is to provide an improved method and apparatusfor continuously casting hollow rounds and overcoming problemsencountered heretofore.

A further object is to provide a method and apparatus of the foregoingtype in which 1 subject both the inside and outside surfaces of ahollow-round casting to water sprays, and in which I employ an improvedtechnique for maintaining the inside skin in a concentric relation withthe outside skin.

A more specific object is to provide an improved method and apparatusfor continuously casting hollow rounds in which I employ magnetic meansfor detecting any eccentricity of the inner skin, and additionalmagnetic means for correcting such eccentricity.

In the drawings:

FIGS. 1 and 10 together are a vertical sectional view of an apparatusfor continuously casting hollow rounds in accordance with my invention;

FIG. 2 is a side elevational view of the mechanism embodied in theapparatus for handling the starter bar;

FIG. 3 is a vertical sectional view of a portion of my novel lanceextension and magnetic positioning mechanism for maintaining the insideskin of the casting in concentric relation with the outside skin;

FIG. 4 is an exploded side elevational view, partly in section, of theupper portion of the starter bar and its detachable stool;

FIG. 5 is a horizontal section on line V-V of FIG. 3; and

HG. 6 is a schematic wiring diagram.

FIGS. 1 and la together show an open-ended tubular mold l and a tubularlance 12 extending through the mold. leaving an annular cavity l3therebetween. The mold is fixed to vertically spaced pairs of beams 14.The lance is suspended from a ball joint 15 carried by a pair of beams16 spaced above the first-named beams. Oscillating mechanisms 17 and 18are connected to beams 14 and 16 respectively for oscillating the beams,mold and lance up and down in unison, as is commonly done with moldsused for continuously casting products of solid cross section. Sincesuitable oscillating mechanisms are well known, I have indicated themonly diagrammatically. A hollow round casting C is shown emerging fromthe bottom of the mold. After leaving the mold, the casting passesthrough conventional guide rolls [9 and water sprays 20. Farther downthe casting passes through conventional pinch rolls and bending rolls,not shown.

A refractory lined tundish 21 and one or more refractory lined troughs22 are supported above the top of mold 10 in the space between the moldand beams 16. The tundish is of U- shape in plan and has a centralpassage 23 to accommodate lance 12, which passage has a sufficientlylarge inside dimension not to interfere with oscillation of the lance.The bottom wall of the tundish has pouring nozzles 24 corresponding innumber to troughs 22 and positioned above the respective troughs. Thetundish contains a supply of molten metal M, which may be introducedfrom any suitable ladle or the like, not shown. Flow of metal throughthe nozzles is controlled by gates 25 slidably supported on the bottomof the tundish. The troughs slope downwardly toward the mold todischarge metal continuously into the annular cavity 13 between the moldand lance.

Before I start a casting operation, I insert a tubular starter bar 26and detachable annular stool 27 into the bottom of the annular cavity13. FIGS. 2 and 4 show a preferred construction of starter bar andmechanism for handling it. The upper end of the starter bar is ofreduced diameter and fits within a groove 28 in the bottom face of thestool. The stool has a plurality of radial bolts 29 which span itsgroove 28. The upper edge of the starter bar has a series of upwardlyopen L-shaped slots 35 which receive bolts 29 in their horizontalsegments to connect the stool to the starter bar. The upper face of thestool carries a plurality of upstanding bolts 36. As molten metal fillsthe annular mold cavity 13, the starter bar and stool are withdrawncontinuously from the mold. The bolts 36 become embedded in thepartially solidified casting and thus attach the stool to the casting.At the proper point in the descent of the casting, l rotate the starterbar through a small arc to disconnect it from the stool. Such rotationaligns the vertical segments of slots 35 with bolts 29. The starter barthen descends more rapidly than the casting and pulls free from itsstool 27. The latter continues on with the casting through the bendingrolls, etc.

As FIG. 2 shows, the mechanism for handling the starter bar 26 includesa stand 37 located below the guide rolls 19. The upper end of the standcarries a set of pinch rolls 38, motors 39 for driving these pinch rollsand fluid-pressure cylinders 40 for advancing or retracting the pinchrolls into or out of engagement with the starter bar. I mount a table 41within the lower portion of the stand and connect this table withupstanding fluid-pressure cylinders 42 fixed to the outside of the standfor raising and lowering it. The table carries a rotatable head 43 and apair of fluid-pressure cylinders 44 connected to the head throughsuitable linkages or gearing for rotating the head through a small arcin either direction. The head carries a pair of pivoted gripper arms 45.A fluid-pressure cylinder 46 interconnects the two arms. The variouscylinders have the usual connections and controls (not shown) foradmitting and discharging fluid.

To raise the starter bar 26 preliminary to beginning a castingoperation, I operate cylinders 40 to engage the pinch rolls 38 with thestarter bar, and I operate motor 39 to drive these pinch rolls. At thistime the gripper arms 45 are disengaged from the bar, and I operatecylinders 42 to raise the table 41 and head 43 to their uppermostposition. When the casting operation begins, I retract the pinch rolls38. Just before the lower end of the casting reaches the position atwhich the starter bar is to be disconnected, I operate cylinder 46 tomove the gripper arms 45 into engagement with the starter bar.Thereafter I operate cylinders 44 to rotate the starter bar through thearc necessary to align the vertical segments of slots 35 with bolts 29,as already described. I release the pressure in cylinders 42, whereuponthe starter bar drops free.

As FIG. 1 shows, mold includes an internal replaceable sleeve 49,preferably of copper, spaced from its outer wall. Annular horizontalpartitions 50 divide the space between the sleeve and the outer wall ofthe mold into a plurality of comartments 51. Preferably l mountvertically extending annular baffles 52 within these compartments. Thelower and upper portions of the compartments have water inlets 53 and 54respectively. The lance 12 includes an outer replaceable sleeve 55, alsopreferably of copper, and spaced concentric outermost, intermediate andinnermost tubes 56, 57 and 58 within the sleeve. The tubes define watercirculating passages between the sleeve and the innermost tube 58. lconnect a water inlet 59 and outlet 60 with the upper portions of theoutermost tube 56 and intermediate tube 57 respectively. I connectanother water inlet 61 with the upper end of the innermost tube 58.

As FIG. 3 shows, I suspend a tubular lance extension 64 from a balljoint 65 at the bottom of lance 12. The lance extension is formed of twosections connected end-to-end with a ball joint 66. The lance extensioncommunicates with the innermost tube 58 of the lance. Water introducedto the innermost tube flows downwardly through this tube and throughlance extension and discharges through nozzles 67 in the latter.

With the construction thus far described, molten metal poured into theannular cavity 13 is chilledon its outside by water which circulatesaround the sleeve 49. This metal is chilled on its inside by water whichcirculates within sleeve 55, and by water discharging through nozzles67. Additional water may be sprayed on the outside of the castingbeneath the mold through conventional nozzles 20, as already described.This arrangement solidifies outside and inside skins E and l ofprogressively increasing thickness on the casting, leaving a liquid coreL between the two skins. At some distance below the mold the castingsolidifies throughout. My invention, as hereinafter described, overcomesa problem that the two skins tend not to remain perfectly concentric asthe casting travels between the bottom of the mold and the level atwhich the casting solidifies throughout.

In accordance with my invention, l mount an annular watercooled plug 68on the upper section of the lance extension 64 and two similar plugs 69and 70 on the lower section of the lance extension (FIG. la). Theuppermost plug 68 lies just below the ball joint 65 and only a shortdistance below the mold 10. The lowermost plug 70 lies just above thelevel at which the product solidifies throughout. The plugs are ofmagnetic material, preferably mild steel. The inside skin of the castingrides against the plugs, whereby the plugs serve to position this skin.

l mount a first opposed pair of positioning magnets 71 and 71a and asecond such pair 72 and 72a opposite the uppermost plug 68 adjacent theoutside skin arranged as FIG. 5 shows. Immediately above the two pairsof positioning magnets, l mount similarly arranged pairs of detectingmagnets, one pair of which is shown at 73, 73a in FIGS. 1 and 6. l mountsimilar positioning and detecting magnets opposite each of the otherplugs 69 and 70, but I have not repeated the description. Since thecasting is hot and above its Curie point, it has negligible magneticeffect even though it may be of ferrous material. lf the inside skintends to become eccentric at any level, one or more pairs of detectingmagnets detect the fact that the corresponding plug 68, 69 or 70 isoff-center with respect to the magnets, whereupon the corresponding pairof positioning magnets act to pull the plug back to its centeredposition and restore concentricity.

l have shown the positioning magnets arranged with their poles in thesame horizontal plane, which is the arrangement I use for castings ofrelatively large diameter (for example 10 inches or more). For smallerdiameters, flux leakage and spacer limitations make this arrangementless practical. Hence 1 may place each magnet with its poles in the samevertical plane, one above the other.

FIG. 6 shows schematically the electric circuit in which I connect onepair of positioning magnets 71 and 71a and the corresponding pair ofdetecting magnets 73 and 73a. The circuits for the other magnets aresimilar. Magnets 71 and 71a have windings 76 and 76a. Magnets 73 and 73ahave windings 77 and 77a. l energize the circuit from a suitable ACpower source connected to lines 78.

I connect the primary winding of a transformer 79 across lines 78. 1connect one end of the secondary winding of the transformer with one endof each winding 77 and 770 on the detecting magnets 73 and 73a throughrespective capacitors 80 and 80a. 1 connect the other end of thesecondary winding with the other end of the windings 77 and 770 throughresistors 81 and 81a respectively. I ground this end of the secondarywinding, as indicated at 82. I connect a larger resistor 83 and a solidstate rectifier 84 in series with each other and in parallel withresistor 81, and a similar resistor 83a and rectifier 84a in parallelwith resistor 81a.

As long as plug 68 is centered, the two windings 77 and 770 are in astate of near-resonance with their series capacitors 80 and 80a. Thewinding and capacitor pass current through resistors 81 and 81a andproduce an AC voltage drop therethrough. The addition of resistors 83and 83a in series with rectifiers 84 and 84a permit pick-up of a DCvoltage drop at measuring output terminals 85 and 850. Under a balancedcondition terminals 85 and 85a are at equal small positive potentialwith respect to ground. If, for example, plug 68 is displaced to theleft, the air gap between the plug and the detecting magnet diminishes,the inductance of this side of the circuit increases, and the circuitceases to be in resonance. A smaller current flows through resistor Blthan through resistor 810, thus lowering the positive potential atterminal 85 and raising the potential at terminal 854:.

I connect the power input terminals of DC power amplifiers 88 and 88aacross lines 78. l connect the power output terminals of theseamplifiers to the respective windings '76 and 76a of the positioningmagnets 71 and 710. I connect the control terminals of the amplifiers toterminals 85 and 85a and to grounds as indicated at 89 and 89a. When thepotential at terminal 85 drops as described, the current through winding76 drops and magnet 71a exerts a stronger force on the plug than magnet7]. In this manner the plug returns to a concentric position and theresonance of the circuit is restored. Similar action takes place at anyof the other magnets to maintain the plugs concentric at all times.

From the foregoing description, it is seen that my invention affords asimple reliable method and apparatus for continuously casting hollowrounds and maintaining a uniform wall thickness. The magnetic meansassures that the plugs remain centered in the casting and thus preventany non-uniformity.

lclaim:

l. A method of continuously casting a hollow-round comprising pouringmolten metal continuously into an annular mold cavity, cooling theoutside and inside surfaces of the metal within the mold and therebyforming outside and inside skins on the hollow-round within the moldleaving a liquid core between said skins, continuously withdrawing thepartially solidified hollow-round from the bottom of the mold overwater-cooled plugs of magnetic material, continuing the cooling of bothsurfaces of the hollow-round until the hollowround solidifies throughoutat a level spaced below the mold, detecting any eccentricity of theinside skin between said mold and said level, and correctingmagnetically with said plugs such eccentricity.

2. A method as defined in claim 1 in which said plugs are acted onmagnetically to detect eccentricity of said inside skin.

3. A method as defined in claim 1 in which a tubular starter bar isinserted in said mold from beneath preliminary to commencing a castingoperation, and is disconnected from the partially solidifiedhollow-round by rotating it through a small arc.

4. Apparatus for continuously casting a hollow-round comprising atubular watercooled mold, a water-cooled lance suspended within saidmold leaving an annular cavity therebetween, means for pouring moltenmetal into said cavity, whereby a partially solidified hollow-roundhaving solidified outside and inside skins and a liquid core emergesfrom the bottom of said mold, which hollow-round solidifies throughoutat a lower level, an extension on said lance below said mold, at leastone water-cooled plug of magnetic material on said extension between thebottom of said mold and the level at which the hollow-round solidifiesthroughout, said plug being of a shape to ride against said inside skin,and magnetic means outside the hollow-round for maintaining said plugand said inside skin in a concentric relation with said outside skin.

5v Apparatus as defined in claim 4 in which said magnetic means includesopposed pairs of detecting magnets and positioning magnets opposite saidplug, said detecting magnets responding to any shift in the position ofsaid plug to change the attractive force exerted by said positioningmagnets to restore said plug to a position concentric with said outsideskin.

6. Apparatus as defined in claim 4 in which said extension is formed insections, and including ball joints connecting said extension with saidlance and said sections end-to-end, there being at least one plug oneach section and corresponding magnetic means opposite each plug.

7. Apparatus as defined in claim 6 in which said extensions are tubularfor conducting cooling water to said plugs, and including nozzlescarried by said extensions for applying cooling water to the inside ofthe hollow-round below the mold.

8. Apparatus as defined in claim 4 including a tubular starter bar, astool carried by said bar, means for inserting said starter bar into thebottom of said cavity, and means for rotating said starter bar through asmall arc to disconnect it from said stool.

9. Apparatus as defined in claim 8 in which said starter bar has aplurality of L-shaped slots in its upper edge and said stool has boltsreceived in said slots for connecting the stool and starter bar.

t i i i

1. A method of continuously casting a hollow-round comprising pouringmolten metal continuously into an annular mold cavity, cooling theoutside and inside surfaces of the metal within the mold and therebyforming outside and inside skins on the hollowround within the moldleaving a liquid core between said skins, continuously withdrawing thepartially solidified hollow-round from the bottom of the mold overwater-cooled plugs of magnetic material, continuing the cooling of bothsurfaces of the hollowround until the hollow-round solidifies throughoutat a level spaced below the mold, detecting any eccentricity of theinside skin between said mold and said level, and correctingmagnetically with said plugs such eccentricity.
 2. A method as definedin claim 1 in which said plugs are acted on magnetically to detecteccentricity of said inside skin.
 3. A method as defined in claim 1 inwhich a tubular starter bar is inserted in said mold from beneathpreliminary to commencing a casting operation, and is disconnected fromthe partially solidified hollow-round by rotating it through a smallarc.
 4. Apparatus for continuously casting a hollow-round comprising atubular water-cooled mold, a water-cooled lance suspended within saidmold leaving an annular cavity therebetween, means for pouring moltenmetal into said cavity, whereby a partially solidified hollow-roundhaving solidified outside and inside skins and a liquid core emergesfrom the bottom of said mold, which hollow-round solidifies throughoutat a lower level, an extension on said lance below said mold, at leastone water-cooled plug of magnetic material on said extension between thebottom of said mold and the level at which the hollow-round solidifiesthroughout, said plug being of a shape to ride against said inside skin,and magnetic means outside the hollow-round for maintaining said plugand said inside skin in a concentric relation with said outside skin. 5.Apparatus as defined in claim 4 in which said magnetic means includesopposed pairs of detecting magnets and positioning magnets opposite saidplug, said detecting magnets responding to any shift in the position ofsaid plug to change the attractive force exerted by said positioningmagnets to restore said plug to a position concentric with said outsideskin.
 6. Apparatus as defined in claim 4 in which said extension isformed in sections, and including ball joints connecting said extensionwith said lance and said sections end-to-end, there being at least oneplug on each section and corresponding magnetic means opposite eachplug.
 7. Apparatus as defined in claim 6 in which sAid extensions aretubular for conducting cooling water to said plugs, and includingnozzles carried by said extensions for applying cooling water to theinside of the hollow-round below the mold.
 8. Apparatus as defined inclaim 4 including a tubular starter bar, a stool carried by said bar,means for inserting said starter bar into the bottom of said cavity, andmeans for rotating said starter bar through a small arc to disconnect itfrom said stool.
 9. Apparatus as defined in claim 8 in which saidstarter bar has a plurality of L-shaped slots in its upper edge and saidstool has bolts received in said slots for connecting the stool andstarter bar.